Video Lecture
Theory For Notes Making
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Objective Assignment
1.
Magnets cannot be made from which of the following substances
(a) Iron
(b) Nickel
(c) Copper
(d) All of the above
Ans (c)
2.
The magnetic moment of atomic neon is
(a) Zero
(b) \mu B/2
(c) \mu B
(d) 3\mu B/2
Ans (a)
3.
Which of the following is most suitable for the core of electromagnets (a) Soft iron
(b) Steel
(c) Copper-nickel alloy
(d) Air
Ans (a)
4.
Substances in which the magnetic moment of a single atom is not zero, is known as
(a) Diamagnetism
(b) Ferromagnetism
(c) Paramagnetism
(d) Ferrimagnetism
Ans (c)
5.
If a diamagnetic solution is poured into a U-tube and one arm of this U-tube placed between the poles of a strong magnet with the meniscus in a line with the field, then the level of the solution will
(a) Rise
(b) Fall
(c) Oscillate slowly
(d) Remain as such
Ans (b)
6.
The magnetic susceptibility does not depend upon the temperature in
(a) Ferrite substances
(b) Ferromagnetic substances
(c) Diamagnetic substances
(d) Paramagnetic substances
Ans (c)
7.
The magnetic susceptibility is negative for
(a) Paramagnetic materials
(b) Diamagnetic materials
(c) Ferromagnetic materials
(d) Paramagnetic and ferromagnetic materials
Ans (b)
8.
Curie temperature is the temperature above which
(a) A paramagnetic material becomes ferromagnetic
(b) A ferromagnetic material becomes paramagnetic
(c) A paramagnetic material becomes diamagnetic
(d) A ferromagnetic material becomes diamagnetic
Ans (b)
9.
A frog can be deviated in a magnetic field produced by a current in a vertical solenoid placed below the frog. This is possible because the body of the frog behaves as
(a) Paramagnetic
(b) Diamagnetic
(c) Ferromagnetic
(d) Antiferromagnetic
Ans (b)
10.
Which one of the following is a non-magnetic substance
(a) Iron
(b) Nickel
(c) Cobalt
(d) Brass
Ans (d)
11.
Liquid oxygen remains suspended between two pole faces of a magnet because it is
(a) Diamagnetic
(b) Paramagnetic
(c) Ferromagnetic
(d) Antiferromagnetic
Ans (b)
12.
For an isotropic medium B, m, H and M are related as (where B,\,\,{{\mu }_{0}},\,\,H and M have their usual meaning in the context of magnetic material
(a) (B-M)={{\mu }_{0}}H
(b) M={{\mu }_{0}}(H+M)
(c) H={{\mu }_{0}}(H+M)
(d) B={{\mu }_{o}}(H+M)
Ans (d)
Subjective Assignment
Q.1
The permeability of magnetic materials is 0.9983. Name the type of magnetic materials it represents.
Q.2
The susceptibility of a magnetic material is \displaystyle 1.9\,\times \,{{10}^{{-5}}}. Name the type of magnetic materials it
Q.3
Which of the following substances are diamagnetic ? Bi, Al, Na, Cu, Ca and Ni
Q.4
Mention the two characteristic properties of the material suitable for making core of a transformer.
Q.5
Give two essential characteristics of a material used for preparing an electromagnet.
Q.6
Why do we prefer to use the alloy alnico for making permanent magnets?
Q.7
What is a non magnetic material?
Q.8
The susceptibility of a magnetic material is \displaystyle 1.9\,\times \,{{10}^{{-5}}}. What type of material does it represent?
Q.9
The susceptibility of a magnetic material is \displaystyle -4.2\times \,{{10}^{{-6}}}. What type of material does it represent?
Q.10
The relative magnetic permeability of a magnetic material is 800. Identify the type of material.
Q.11
Two substances A and B have relative permeabilities slightly greater and less than unity respectively. What is their magnetic nature?
Q.12
Susceptibility of iron is more than that of copper. What does this statement imply?
Q.13
What happens when a diamagnetic substance is placed in a varying magnetic field?
Q.14
How does the intensity of magnetization of a paramagnetic material vary with increasing applied magnetic field?
Q.15
Why do magnetic lines of force prefer to pass through ferromagnetic materials?
Q.16
Out of the following, identify the materials which can be classified as (i) paramagnetic, (ii) diamagnetic :
(a) Aluminium
(b) Bismuth
(c) Copper
(d) Sodium
Write one property to distinguish between paramagnetic and diamagnetic materials.
Q.17
Draw magnetic field lines when a (i) diamagnetic, (ii) paramagnetic substance is placed in an external magnetic field. Which magnetic property distinguishes this behaviour of the field lines due to the two substances ?
Q.18
If Y stands for the magnetic susceptibility of a given material, identify the class of material for which (i) \displaystyle -1\ge \,\chi <0
(ii) \displaystyle 0<\,\chi <\in (stands for a small positive number).
Q.19
(a) How does a diamagnetic material behave when it is called to very low temperatures ?
(b) Why does a paramagnetic sample display greater magnetization when cooled ? Explain
Q.20
State two characteristic properties distinguishing the behavior of paramagnetic and diamagnetic materials.
Q.21
(a) How is an electromagnet different from a permanent magnet ?
(b) Write two properties of a material which make it suitable for making electromagnets.
Q.22
Depict the behavior of magnetic field lines when (i) a diamagnetic material and (ii) a paramagnetic material is placed in an external magnetic field. Mention briefly the properties of these materials which explain this distinguishing behavior.
Q.23
What is the basic use of hysteresis curve?
Q.24
An iron bar magnet is heated to 1000ºC and then cooled in a magnetic field free space. Will it retain magnetism?
Q.25
Identify the materials, which can be classified as paramagnetic and diamagnetic : Al, Bi, Cu, Na.
Q.26
identical specimens of magnetic materials nickel, antimony and aluminium are kept in a non-uniform magnetic field. Draw the modifications in the field lines in each case. Justify your answer.
Q.27
What is the susceptibility and permeability of a perfectly diamagnetic substance?
Q.28
Which material is used to make electromagnets and why?
Q.29
In what way is the behaviour of a diamagnetic material different from that of a paramagnetic material, when kept in an external magnetic field?
Q.30
paramagnetism on the basis of electron theory.
Q.31
Distinguish between dia and para magnetic substances.
Q.32
Define the term retentivity and coercivity.
Q.33
Explain magnetic properties of soft iron and steel.
Q.34
Write any two differences between electromagnet and permanent magnet.
(a) The earth’s core is known to contain iron. Yet geologists do not regard this as a source of the earth’s magnetism. Why?
(b ) Would the maximum possible magnetisation of a paramagnetic sample be of the same order of magnitude as the magnetization of a ferromagnet?
(c) Explain qualitatively on the basis of domain picture the irreversibility in the magnetisation curve of a ferromagnet.
(d) The hysteresis loop of a soft iron piece has a much smaller area than that of a carbon steel piece. If the material is to go through repeated cycles of magnetisation, which piece will dissipate greater heat energy?
(e) ‘A system displaying a hysteresis loop such as a ferromagnet, is a device for storing memory?’ Explain the meaning of this statement.
(f) What kind of ferromagnetic material is used for coating magnetic tapes in a cassette player, or for building ‘memory stores’ in a modern computer?
Q.35
Define magnetizing field, magnetic induction, permeability, intensity of magnetization and susceptibility. Establish relation between permeability and susceptibility.
Q.36
Distinguish between the magnetic properties of dia, para and ferromagnetic substances in terms of (i) susceptibility. (ii) magnetic permeability and (iii) coercivity. Give one example of each of these materials.
Draw the field lines due to an external magnetic field near a (i) diamagnetic. (ii) paramagnetic substance.
Q.37
What are dia, para and ferro magnetic materials? Discuss their important properties.
Q.38
Discuss briefly electron theory of magnetism. How does it account for the three kinds of behaviour of magnetic substances?
Q.39
What is meant by hysteresis ? Discuss briefly the dissipation of energy due to hysteresis. Draw hysteresis curves of soft iron and steel.
Q.40
If maximum value of permeability of -metal is 0.126 Tm, what will be the maximum relative permeability and susceptibility of the metal?
Q.41
A sample of paramagnetic salt contains 2.0 × 1024 atomic dipoles each of dipole moment 1.5 × 10–23 J T–1. The sample is placed under a homogeneous magnetic field of 0.64 T, and cooled to a temperature of 4.2 K. The degree of magnetic saturation achieved is equal to 15%. What is the total dipole moment of the sample for a magnetic field of 0.98 T and a temperature of 2.8 K? (Assume Curie’s law)
Q.42
A Rowland ring of mean radius 15 cm has 3500 turns of wire wound on a ferromagnetic core of relative permeability 800. What is the magnetic field B in the core for a magnetising current of 1.2 A?
Q.43
A magnetizing field of 1500 A/m produces a flux of \displaystyle 2.4\,\times \,{{10}^{{-5}}} weber in a bar of iron of cross- sectional area 0.5 \displaystyle c{{m}^{2}}. Calculate the permeability and susceptibility of the iron bar used.
Q.44
The magnetic field B and the magnetic intensity H in a material are found to be 1.6 T and
1000 A/m respectively. Calculate the relative permeability \displaystyle {{\mu }_{r}} and the susceptibility \displaystyle {{\chi }_{m}} of material.
Q.45
For a magnetizing field of intensity \displaystyle 2\,\times \,{{10}^{3}} \displaystyle A{{m}^{{-1}}}, aluminium at 280 K acquires intensity of magnetization of \displaystyle 4.8\,\times \,{{10}^{{-2}}} \displaystyle A{{m}^{{-1}}}. Find the susceptibility of aluminium at 280 K. If the temperature of the metal is raised to 320 K, what will be its susceptibility and intensity of magnetization?
Q.46
Answer the following questions:
(a) Why does a paramagnetic sample display greater magnetization (for the same magnetising field) when cooled?
(b) Why is diamagnetism, in contrast, almost independent of temperature?
(c) If a toroid uses bismuth for its core, will the field in the core be (slightly) greater or (slightly) less than when the core is empty?
(d) Is the permeability of a ferromagnetic material independent of the magnetic field? If not, is it more for lower or higher fields?
(e) Magnetic field lines are always nearly normal to the surface of a ferromagnet at every point. (This fact is analogous to the static electric field lines being normal to the surface of a conductor at every point.) Why?
(f) A certain region of space is to be shielded from magnetic fields. Suggest a method.
(g) What happens if an iron bar magnet is melted? Does it retain its magnetism?
Q.47
(i) Write two characteristics of a material used for making permanent magnets.
(ii) Why is core of an electromagnet made of ferromagnetic materials ?
Q.48
A uniform magnetic field gets modified as shown in fig. When two specimens X and Y are placed in it. Identify the specimens X and Y are placed in it. Identify the specimens X and Y.
